Schematic Drawing


Jim, N5IB
 

The recent schematic puzzle dredged up one of my 'pet peeves' about published schematic drawings. Namely the often inconsistent, occasionally incorrect, use of the drawing conventions for intersecting wires. It can leave the reader puzzling over the intent of the person who made the drawing. The schematic that was posted for the puzzle did contain a few instances of use/non-use of the dot convention that could be confusing to folks new to reading schematics. There's an especially troubling one at the base of the 8050 transistor.

I had recently reviewed the schematic I'd drawn for the Bayou Jumper and spotted a couple of places where I'd accidentally left an unneeded dot. Fortunately not one that changed the meaning. There was also an actual real wire error in the revD TX drawing. Those have been fixed and will shortly be re-posted to the kit web page.

So with my battered 'curmudgeon hat' firmly in place, and with apologies to Capt Jack Sparrow, I offer my 'guidelines', not to be confused in any way with 'rules' LOL

a) when wires meet and should be connected, put a dot
b) avoid 4-way intersections, offset them slightly
c) hark back to the old-school 'bridge' to clearly show a no-connection crossover

Fortunately these are easily implemented in the free ExpressSCH schematic capture software.
The attached PDF image shows examples.

73,
Jim, N5IB


John Clements
 

I am probably also guilty of missing the dot and prefer the old school bridge method myself.  As far as I know KiCad does not offer a bridge and either crosses over the wire or ends a connection with a dot.  May I also offer option D using labels when possible.  Example below where the DTR wire would have to jump over several wires and start to look a little messy.
73 John kc9on


Rick Bennett
 

Jim, great pointers!  I do like the "bridge" for no-connection.  I have been using KiCad, not sure if it can do the bridge.  Another thing is if possible to route the wires so they do not cross at all, I know this can be difficult, but not always impossible.

Rick, KC0PET


Bob Groh wa2cky
 

Now retired, I spent over 50 years (egad!! time flies) in the electronics design world as an engineer and designer.  I do NOT recommend using the 'hoop' - it is not accepted by any schematic drawing software nor anyone in the industry.

I simply use the rule that 2 wires crossing (dot or not) are NOT connected. No exceptions. If you want to show two wires connecting, you dead end one into the other (with or without a dot).


Sorry for the drawing!  Too early in the morning!

73, Bob Groh, WA2CKY


Tim N9PUZ
 

John,

My comment on schematics that use labels is yes, they can clean up schematic clutter. However, when you see a label like your example on a large schematic there is no way of knowing how many places it may connect if you are looking at a paper copy or a non-searchable PDF.

Tim N9PUZ

On Tue, Aug 16, 2022 at 8:36 AM John Clements <jwc123@...> wrote:
I am probably also guilty of missing the dot and prefer the old school bridge method myself.  As far as I know KiCad does not offer a bridge and either crosses over the wire or ends a connection with a dot.  May I also offer option D using labels when possible.  Example below where the DTR wire would have to jump over several wires and start to look a little messy.
73 John kc9on


O-B-1
 

The wiring schematics that we used for the U-2R reconnaissance aircraft in the US Air Force were in a binder about 6 inches thick, and when unfolded to full length were about the same length as the aircraft.

I once traced a problem that seemed to be in the very tail of the aircraft, and when I had found the issue it was a component in the very nose of the aircraft loading the circuit down. It took nearly 12 hours of tracing and continuity/checks, isolating segments in the circuit, back to front.

To say the least, that one problem made me very familiar with both, the schematics AND the wiring harness of the aircraft.

73 de KJ7WUZ (Dave)